Optical measurement of blood hematocrit on medical tubing with dual wavelength and detector model

Blood hematocrit (Hct) is a clinically important index to detect death-dealing symptoms such as anemia and thrombosis, especially for patients with artificial heart, in dialysis and during open-heart surgery. Optical technology has been applied to monitor hematocrit noninvasively, continuously and conveniently, however, it was not well established for actual use. The purpose of this study is to develop an accurate and stable optical hematocrit measurement without any calibrations for device-mounting errors. To this end, we propose a theoretical method. In this method, disturbances are cancelled by using dual detector and optical path changes are calibrated by dual wavelength so that we can measure hematocrit without calibrations of these. Based on the method, a measurement unit that has two LEDs (805/1300[nm]) and four photo detectors was developed. Then, we performed experiments with 38 blood samples from five bovines' blood (Hct: 19-55%). These blood samples were circulated in a mock-up circuit by a blood pump. During the experiment, we measured hematocrit on medical tubing with the developed measurement system. As a result, we could measure hematocrit within 1.7 Hct% mean errors for 38 blood samples without any calibrations. The result indicates that the proposed method is applicable for hematocrit measurement on medical tube in enough small error. We found this proposed method is effective for developments of clinically workable hematocrit measurement/monitoring system.